Multigrid tube regenerative circuit



Feb. 2, 1937. K. STEIMEL MULTIGRID TUBE REGENERATIVE CIRCUIT Filed June 1, 1953 2 Sheets-Sheet 1' INVENTOR KARL STEIMEL BY Mg ma, ATTORNEY Feb. 2, 1937. K. STEIMEL MULTIGRID TUBE REGENERATIVE CIRCUIT Filed June 1, 1933 2 Sheets-Sheet 2 INVENTOR KARL STEIMEL K6 Patented Feb. 2, 1937 UNITED STATES MULTIGRID TUBE REGENERATIVE CIRCUIT Karl Steimel, Berlin, Germany, assignor to Telefunken Gesellschaft fur Drahtlose Telegraphic m. b. H., Berlin, Germany Application June 1, 1933, Serial No. 673,850

In Germany 8 Claims.

The present invention relates to high frequency networks using multi-grid tubes, and especially to such networks wherein feed-back is employed between electrodes.

The usual feed-back circuits operate in such manner that a portion of the anode alternating potential is impressed at the proper phase upon the control grid. In the feed-back coupling for regeneration, the feed-back potential is added to the control voltage. The amplification value, and selectivity, of ahigh frequency amplifier stage can be considerably increased by artificially regenerating the anode circuit. In this case the impedance of the circuit increases, and the inner impedance of the tube will be compensated by the negative resistance corresponding with the amount of regeneration. However, such feed back coupling is only suitable in case of a succeeding rectifier stage, i. e., if there exists no longer a high frequency impedance in the anode circuit of the succeeding tube, since, otherwise due to the various detrimental side effects which the back coupling arrangement implies, such as undesired capacities, cross couplings appear causing parasitic oscillations. In particular in case of high frequency amplification with screen grid tubes having a high inner impedance, feed-back coupling is practically impossible.

In accordance with the present invention the great advantage of de-tuning of the anode circuit is obtained without reaction upon the control grid. It is the object of the invention, then, to provide feed-back couplings which although they act upon a grid electrode of the tube do so in such a way as to produce no reaction on the control grid to which the signal voltage is applied.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims, the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawings in which I have indicated diagrammatically several circuit organizations whereby my invention may be carried into effect.

In the drawings,

Fig. 1 diagrammatically shows a regenerative amplifier circuit employing the invention,

Fig. 2 diagrammatically shows a regenerative amplifier circuit employing a modification,

Fig. 3 diagrammatically shows an oscillatorconverter modification,

Figs. 4 and 5 diagrammatically show two further modifications of the invention using regeneration between grid elements of a tube.

Referring now to the drawings, wherein like reference characters in the different figures correspond to similar circuit elements, in Fig. 1.

June 23, 1932 is shown a tube I having three grids placed between anode and cathode. The middle grid 2 is a screen grid, the incoming alternating signal control voltage, derived from antenna circuit 3, being impressed upon the first grid 4, while upon the third grid 5 a feed-back coupling voltage, derived from the anode circuit, is impressed. Due to the feed-back coupling M, and its effect on the third grid 5, the damping of the tuned anode circuit 6 is decreased. On account of the screen grid 2 the back coupling effect of the anode potential upon the control grid 4 is prevented.

In arranging the individual similarly tuned scillatory circuits 6 and 1 within casings shielded against each other, as shown in the figures by thick lines 8, in this manner a practically complete de-coupling between the two oscillatory circuits is insured. Since the third grid is controlled at opposite phase to the anode, it operates in phase with the first grid. Due to the control at opposite phase to the anode the reaction of the anode potential upon the control grid is still further reduced than hitherto possible by means of the screen grid.

It is even possible that the screen grid may be entirely dispensed with. In this case the alternating grid potential at the second grid which now is the back coupling grid, must be so tuned that the anode reaction is completely compensated in the manner of a neutralizing arrangement. It is possible to simultaneously combine with this back coupling circuit a neutralization within the tube. In the event that the inner neutralization is not yet sufficient it can still be completed outside of the tube in that a very small variable capacity N is placed between the second and the first grid by which a complete neutralization as it is understood, is possible. This condenser only enables an additional small correction in regard to the neutralization already present in the tube. Whether a screen grid is de-' sired between the two control grids, or neutralization, depends upon whether the greater stability of a screen grid arrangement is preferred, or whether one chooses the simpler double grid construction of the tube.

Especially advantageous is the use of a tube (see Fig. 2) having a cathode, four grids and an anode. This arrangement is to be so designed that the first grid 4 of the tube l forms a signal control grid, while the second grid 2 serves as screen grid, and the third grid is used as the output electrode. Thus the fourth grid 5' is the auxiliary grid to which the back coupling potential is applied, and the outer anode has a positive potential applied thereto. The fourth grid is, in

the current of the third grid electrode decreases when the potential of the fourth grid electrode becomes more positive; since a larger current flows towards the anode electrode, and the sum-current of the third and fifth electrode is practically constant due to the small or negligible infiuence of the grid 5 on the total emission current.

The current of the third grid electrode decreases when the potential of the fourth grid electrode becomes positive. In such a performance of control it is found that, contrary to the hitherto usual back coupling circuits, the potential, impressed upon the grid by means of back coupling, (in this case the fourth grid electrode), need not be at opposite phase to the anode potential (in the present case the third grid electrode). From this results a particularly simple manner of carrying out the back coupling.

Fig. 2 shows the application of such tube to a high frequency amplification circuit for decreasing the damping of the oscillatory anode circuit 6. The incoming alternating signal control voltage is applied to the first grid 4 nearest the oathode. The second grid is the screen grid. The useful resistance, or load circuit 6, is placed in the circuit of the third grid shown in the figure as an oscillatory circuit tuned to resonance. Both circuits 6 and l are tuned to the same frequency. From the third grid the back coupling voltage is supplied to the fourth grid. As already stated the back coupling voltage must be applied to the fourth grid in the same phase.

This is accomplished in the simplest manner in that a resistance-condenser coupling 9, i0 is used for the fourth grid. The bias of the fourth grid is applied across a leakage resistance 2|. The third grid and the end of the leakage resistance are connected to each 0th r by means of a block condenser. In Fig. 2 the leakage resistance is indicated by a potentiometer, and the fourth grid is connected to the variable contact point 22 thereof. Thus, it is possible to eventually adjust the back coupling until shortly before the beginning of the oscillations. The useful potential for the succeeding tube II (shown in Fig. 1) is suitably tapped across the total coupling resistance l02l, and is applied directly to the grid of the adjacent tube. In this circuit the outer anode electrode must be maintained at constant equi-potential, i. e., it is connected to the cathode for the high frequency in a known manner as by a condenser 23.

Another applicable example in which the blocking of the oscillatory circuit at the anode side against the circuit at the grid side, plays a part, is shown in Fig. 3. In this circuit the tube 1 is used in a superheterodyne receiver circuit as an oscillator-converter, or frequency changer, tube. The incoming signal oscillations, derived from loop circuit 3 tuned to signal frequency, are applied to the grid 4 nearest the cathode. The tunable signal circuit 1 is connected to the signal grid 4. The second grid 2 is again the screen grid. By means of the third and fourth grids 5, 5, the local oscillator frequency is produced.

The fourth grid 5' is at negative equi-potential. The equi-potential of the fourth grid 5' is suitably so adjusted that the tube 1 operates in a bend of the characteristic for the anode electrode of the current being passed, so that at the same time rectification takes place in the tube, and the intermediate frequency can be directly supplied from the circuit of the anode electrode. The back coupling between the third and fourth grids for producing the local oscillation frequency is again obtained by means of a resistance-condenser coupling 9, l0. Thus the two grids operate again in the same phase and since the grid 5 is connected to a source of positive potential through a resonant circuit 6 tuned to the local oscillation frequency, the voltage of these grids will vary at this frequency and this portion of the tube will function as a generator of currents of the frequency to which 6 is resonant. The intermediate frequency is taken from the circuit of the anode electrode across intermediate frequency band filters I 2, I3, and is applied to the following tube Id. The latter functions as an intermediate frequency amplifier.

Fig. 4 shows a further embodiment similar to the one above described. Herein is the tube I with the four grids 4, 2, 5, 5' used for high frequency amplification from the first to the third grid, and for anode rectification by means of the fourth grid 5' and main anode electrode 2|, whereby at the same time back coupling exists between the third and fourth grids. The incoming high frequency alternating signal voltage is applied to the grid 4 nearest the cathode, and the second grid 2 is again the screen grid. The third and fourth grids are, also, herein coupled to each other as regards high frequency, and in such manner that in this case an ohmic resistance 2 is placed in the circuit of third grid 5,

and the high frequency is supplied to the oscillatory circuit in the input line for the fourth grid, across a blocking condenser 9.

The oscillatory circuit 5 in turn is coupled by means of a transformer 20 so as to be able to easily vary the coupling between this circuit and the circuit of grid 5. The bias for the fourth electrode is chosen in such manner that the current to the anode electrode 2| is adjusted upon a sharp bend of the characteristic of the anode current. Thus rectification takes place in the circuit of the anode electrode. The rectification circuit can be modified in a simple manner if instead of anode rectification, grid rectification is applied to the fourth grid 5. The arrangement remains largely the same, the fifth electrode however is maintained at equi-potential, while the audio frequency current is supplied from the circuit of the fourth grid 5. Consequently the bias of the fourth grid 5' must now practically be zero'.

A further embodiment of the invention is shown in Fig. 5. It is here the question of an aperiodic high frequency amplification with a high amplification value. The main problem of an aperiodic high frequency amplification resides in the fact that the coupling resistances are not to exceed about 5000 ohms, since, otherwise, the capacities of the arrangement representing a parallel connection to the coupling resistances make themselves felt too strongly, thus causing a much too unfavorable effect upon the frequency relation of the amplification. However, in order that it be possible to produce a favorable amplification by means of resistances of only a few thousand ohms, either the slope of the amplifier tube must be extraordinarily steep or the inner impedance of the amplifier tube must be negative; furthermore, in the latter case the negative impedance must be of the same value as the coupling resistance.

In the present application as shown in Fig. 5 such negative impedance is obtained by means of back coupling. This back coupling has now become possible, since the alternating potential applied to the fourth grid 5' can have the same 7 phase as that of the third grid 5. A phase reversal such as is necessary in the case of aperiodic high frequency amplification, is not possible in case of a pure resistance coupling. Again an input alternating signal voltage is applied to the first grid 4. As shown in the figure several signal resonant oscillatory circuits 3|], 3|, 32 are placed ahead of the grid 4 so as to obtain a sufficient selection. The second grid 2 of the tube is the screen grid. The third and fourth grids 5, 5' are connected to each other by means of the aforesaid resistance and condenser coupling 9, Ill. The entire alternating voltage of the third grid 5 is applied by condenser 9 to the fourth grid 5' in order to obtain by means of a sufficiently strong back coupling effect, a negative impedance as effectively as possible.

In similar manner, it is possible to also obtain smaller values by means of the coupling resistances. The third grid has again a highly positive equi-potential, and the fourth grid has a weak negative bias; the anode electrode 2| is maintained at a constant positive potential, and should be short-circuited to the cathode as regards high frequency as by a condenser 23. The useful voltage, which may for instance be supplied to the following tube 40, can be tapped at the same point on resistor H! to which the fourth grid 5 is connected.

For the construction of the amplifier tubes to be used it must be considered that in most cases the useful frequency is taken from the outer circuit of the discharge path between cathode and the third grid. Therefore, it is preferable to suitably dimension this grid for receiving greater energies for instance as a high grid bar or as a blackened grid, i. e., as grid having projecting surfaces for heat conduction. It is furthermore, of importance to dimension the grid in such manner that it absorbs very little current at the fifth electrode disposed further outside, in order to enable an intensive control by means of the fourth grid.

While I have indicated and described several systems for carrying my invention into eifect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention as set forth in the appended claims.

What is claimed is:

1. In combination with a source of signals, a tube including a cathode, a signal grid adjacent the cathode, a cold output electrode, a screen grid electrode adjacent the signal grid, an auxiliary cold electrode adjacent the output electrode, said screen grid being disposed between the signal grid and the output and auxiliary electrodes, means for maintaining said screen grid and output electrode at positive voltages with respect to the cathode, a tuned signal circuit connected between the signal grid and cathode and being coupled to the signal source, means for maintaining the auxiliary electrode constantly negatively biased with respect to the entire cathode, a load network connected to the said output electrode, and means for regeneratively coupling the said output electrode to said negatively biased auxiliary electrode.

2. In a system as defined in claim 1, said load network including a circuit tuned to the same frequency as the signal circuit.

3. In a system as defined in claim 1, a plate electrode in said tube, said load network including a circuit tuned to 'a local oscillation frequency, and a beat frequency network being coupled to said plate electrode.

4. In a system as defined in claim 1, said coupling means including a condenser and a resistor connected in series.

5. In a receiver including a tunable signal input circuit, a tube provided with a cathode, a signal grid, a screen grid, a plate and a pair of auxiliary cold electrodes between the screen grid and plate said input circuit being connected to said cathode and signal grid, a tuned circuit coupled to one of the auxiliary electrodes, at source of positive potential connected to said plate, means for impressing a positive potential on said screen grid, a demodulation circuit connecting said cathode and said one auxiliary electrode and means external to said tube for capacitively coupling said auxiliary electrodes.

6. A radio receiver comprising, a signal amplifier tube including a cathode, a plate, a signal grid and a pair of auxiliary cold electrodes between the signal grid and plate, a circuit connecting the signal grid and cathode, a second signal amplifier tube, an aperiodic network coupling the signal grid circuit of the second tube to one of said auxiliary cold electrodes, said network including a resistor and negative bias source in series between said one auxiliary electrode and said cathode, means for maintaining said plate at a substantially constant positive potential, a condenser coupling the two auxiliary electrodes and a source of positive potential connected to the other of said auxiliary electrodes.

'7. In an amplifying device, the combination of a vacuum tube having a cathode, a signal control grid, an anode, an auxiliary grid located between said signal control grid and anode, a screen grid located between said signal control grid and said auxiliary grid, and a fourth grid located adjacent said auxiliary grid, means for applying positive potentials to said anode and screen grid, a circuit tunable to a desired signal frequency connecting said signal control grid and cathode, a tunable circuit having its high potential side directly connected to said auxiliary grid, a source of positive potential connected to the low potential side of said last named circuit, means for causing the voltages of said auxiliary and fourth grids to vary in similar phase and a circuit including a source of negative bias voltage connecting said fourth grid and cathode.

8. In a regenerative amplifier, the combination of a vacuum tube having a cathode, a signal control grid, an anode, a third grid and a fourth grid located between said signal control grid and anode, a screen grid located between said signal control grid and said third grid, a source of steady positive potential connected to said screen grid, a source of positive potential connected to said anode, a feedback connection between said third and fourth grids including a condenser and a resistor and a source of negative polarizing potential connected in series between said third grid and cathode.

KARL STEIMEL. 

